Field of the Invention
The present invention relates to an image reading apparatus including a light source, a reflection member configured to reflect light reflected from an original so as to change a traveling direction of the light, an optical system configured to condense and image the light reflected from the reflection member, and a photoelectric converter configured to receive the light passing through the optical system and convert the light into electric charge. Further, the present invention relates to an image forming apparatus including the image reading apparatus.
Description of the Related Art
In a conventional technology of an image reading apparatus, an image of an original is read in the following manner. That is, a light source irradiates the original with light, and a reflection member (reflection unit) guides the light reflected from the original to a lens optical system. Then, a photoelectric converter converts the light converged by the optical system into an electric signal. The electric signal is read as an image. In this case, if light (external light) from outside the image reading apparatus or light (stray light) not passing through a proper optical path inside the image reading apparatus strikes a photoelectric conversion element, the image of the original cannot be read properly, resulting in a defective image. To avoid this situation, there may be provided a configuration for covering the photoelectric converter (photoelectric conversion unit) to prevent the external light or stray light from entering the photoelectric conversion unit, or a configuration using as many members having a low reflectance as possible.
As for the configuration for covering the photoelectric converter, a configuration in which a light shielding member is disposed between the optical system and the photoelectric converter so that the light shielding member covers the entire optical path between the optical system and the photoelectric converter, or a configuration in which the entire photoelectric converter is simply covered is conceivable. With such a measure as described above, light which does not pass through the lens, such as the external light from outside the image reading apparatus and the stray light unintendedly reflected from any elements other than the proper optical path, can be blocked to some extent to prevent such a light from entering the photoelectric conversion element.
Japanese Patent Application Laid-Open No. 2000-81564 discloses the configuration using a member having a low reflectance. In the invention described in Japanese Patent Application Laid-Open No. 2000-81564, a light absorbing coating of black color is applied to a glossy surface opposite to a light entrance surface of a reflection mirror. The light absorbing member absorbs a non-effective light beam, whereas a light beam reflected without being absorbed by the light absorbing member is returned in a light entrance direction.
However, in the above-mentioned configuration for covering the photoelectric converter or configuration using a member having a low reflectance, it is difficult to completely prevent stray light, which passes through the optical system such as a lens via the vicinity of a proper optical path, from entering the photoelectric conversion element. As a result, there arise various problems in that the color of the image obtained through image reading becomes faint, that ghost occurs, and that the contrast ratio decreases due to decrease in color density.
Note that, as a measure against the stray light, there is a method of narrowing an aperture portion of the light shielding member to ensure an interval close to the width of the proper optical path. Even in this case, the stray light may be reflected from an upper, lower, right, or left wall surface of the light shielding member having the narrowed aperture portion so that the stray light enters the sensor. Therefore, when the aperture portion is simply narrowed, the image quality may be, in some cases, degraded as compared to the image quality before the measure is taken. Thus, the wall surfaces of the aperture portion of the light shielding member cannot easily be disposed in the vicinity of the light beam.